This invention pertains to the art of electrically energized valves and, more particularly, to such valves employed for controlling flow of gaseous fuel to a burner. The invention is particularly applicable to gas fuel valves employing a thermally actuated bi-metal element that deforms in response to electrically energized heating for opening the valve to permit flow of gaseous fuel to the burner and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications and may be advantageously employed in other valve environments and applications.
Commonly assigned U.S. Pat. No. 3,862,820 to Hantack, issued Jan. 28, 1975 and hereby incorporated by reference, provides general background for thermally responsive gas valves now widely used in domestic appliances. Briefly, an igniter, preferably formed of a silicon carbide material displaying a decreased resistance with an increase in temperature, is used in the valve assembly. A normally closed, thermally actuated bi-metal valve is placed in series with the igniter. A constant voltage is applied across the igniter and thermally actuated bi-metal valve, and the properties of the igniter offer an initial high resistance so that only a small amount of current flows therethrough. The igniter is heated due to current flow so that the igniter material decreases its resistance and, thus, current flow increases. Once a preselected current is attained, the thermally actuated bi-metal valve will open since the thermally actuated bi-metal valve receives sufficient current. Fuel may then flow to a burner and the igniter is sufficiently hot so that the fuel is ignited. By controlling the amount of current needed to open the valve, a manufacturer can be assured that the igniter is sufficiently hot. That is, if the valve opens, the igniter must be above ignition temperature or, stated another way, the valve will not open due to insufficient current to the thermally actuated bi-metal valve if the igniter has not reached sufficient ignition temperature.
Further advancements in the gas valve field are illustrated by commonly assigned U.S. Pat. No. 4,508,314 to Hemme, issued Apr. 2, 1985 and hereby incorporated by reference. A valve poppet member is held closed against its corresponding valve seat by a combination of gas pressure in the valve chamber and resiliency of a bi-metal arm. The poppet material does not always accommodate the preload of the bi-metal arm. For example, either deformation of the elastomeric material of the poppet around portions of the connection with the arm or tackiness of the elastomeric material can inhibit elastic return of the material upon initial movement of the bi-metal arm. In such instances, the poppet may be caused to move at the onset of movement of the bi-metal arm under thermal actuation and the poppet may be lifted from the valve seat prematurely.
The U.S. Pat. No. 4,508,314 teaches use of a poppet bead in conjunction with a recess cavity that causes the bi-metal arm to thermally deflect a predetermined amount to effect release of the preload of the arm against the poppet member. At this point, valve opening occurs. The poppet bead absorbs the preload exerted by the bi-metal arm so that the poppet does not stick onto the arm. This arrangement insures that the elastomeric material responds elastically upon initial movement of the bi-metal arm.
The above-noted constructions provide consistent and reliable valve operation. Further studies, though, have revealed that the elastomeric poppets do not separate from the valve seat in identical manner each time they open. More particularly, a wide temperature range, for example, for 32.degree. to 500.degree. F., must be compensated for and calibrated in the bi-metal arm. Under such a wide range of temperature exposures, the bi-metal arm is subject to various bent configurations. In prior art structures, the thermally responsive arm has an aperture or cut-out formed at one end for receipt on a neck or shank of the poppet. A radially outward extending flange of the poppet has a predetermined dimension that abuttingly engages the bi-metal arm on an upper end of the neck. Under one set of conditions, the arm assumes a configuration tending to lift the leading edge of the poppet material from the valve seat. Under a second set of conditions, the arm is distorted to a different bent configuration such that the back edge of the poppet material is lifted from the valve seat. These different bent configurations lead to inconsistent valve opening. The poppet material has a tendency to "tease" relative to the valve seat instead of exhibiting a quick action, popping sensation.
It has, therefore, been considered desirable to overcome the bent configuration and inconsistent valve opening processes experienced in prior art devices and achieve a more consistent, reliable operation of the valve. The subject invention is deemed to meet these needs and other.